1. Field of the Invention
The present invention relates to a color solid-state imaging apparatus, and more particularly to a color solid-state imaging apparatus capable of providing high color resolution in progressive scan reading.
2. Description of the Related Art
In recent years, there has been an increasing demand for a two-dimensional solid-state imaging apparatus used in an image input device for a personal computer and an electronic still camera. Conventionally, a two-dimensional solid-state imaging apparatus has been developed mainly for a video camera. Such a two-dimensional solid-state imaging apparatus basically uses an interlace reading method in which every other pixel is read in a vertical scanning direction. However, unlike the case of being used in a video camera, etc., in the case of being used in a personal computer and a still camera, a two-dimensional solid-state imaging apparatus is required to use a progressive scan reading method in which all the pixels are sequentially read at a time. The progressive scan reading method has the advantage of providing higher vertical resolution of an image obtained by one reading, compared with the interlace reading method.
Various single chip coloring methods for performing a color display using one two-dimensional solid-state imaging apparatus in the progressive scan reading method have been proposed. Various color filter arrangements applicable to the various simple plate coloring methods have also been proposed. Particularly in the case of attaching importance to color reproducibility, it is desired to use primary colors for color filters.
FIG. 17A shows a color filter arrangement 500 including three primary colors of green (G), red (R), and blue (B) used in a two-dimensional solid-state imaging apparatus (progressive scan reading type charge coupled device (CCD)). The color filter arrangement 500 as shown in FIG. 17A is known as a Bayer arrangement, which is described, for example, in xe2x80x9cA ⅓-inch 330 k-pixel Progressive Scan CCD Image Sensorxe2x80x9d by Nakagawa et al., Technical Report of the Institute of Television Engineers, Sep. 22, 1995; xe2x80x9cColor imaging arrayxe2x80x9d, B. E. Bayer, U.S. Pat. No. 3,971,065, etc.
As shown in FIG. 17A, in the color filter arrangement 500, twice as many pixels as those assigned to each of R and B are assigned to G, and G pixels are arranged in a checkered pattern. R and B pixels are arranged in an orthogonal lattice (i.e., lattice in horizontal and vertical directions) at a two-pixel period both in the horizontal and vertical directions. A luminance signal requires high resolution. Therefore, G pixels to which human eyes have high sensitivity are placed so as to occupy a half of all the pixels, whereby the resolution of a luminance signal can be increased.
FIG. 17B shows spatial resolution characteristics (i.e., resoluble regions in each direction in a two-dimensional space) of the respective G, R, and B pixels in the color filter arrangement 500. G pixels which largely occupy the luminance signal are arranged in a checkered pattern, whereby the luminance signal with relatively high resolution is obtained in the horizontal and vertical directions, as shown in FIG. 17B. However, sufficient resolution cannot be obtained in oblique directions.
FIG. 18A shows a color filter arrangement 510 including G, R, and B primary colors used in a two-dimensional solid-state imaging apparatus (CCD which operates in the same way as in a progressive scan reading type CCD). The color filter arrangement 510 as shown in FIG. 18A is described, for example, in xe2x80x9cDigital card cameraxe2x80x9d by Soga et al., Technical Report of the Institute of Television Engineers, Mar. 4, 1993. In the same way as in the color filter arrangement 500 shown in FIG. 17A, twice as many pixels as those assigned to each of R and B are assigned to G which largely occupies the luminance signal in the color filter arrangement 510. However, the G pixels are arranged in a stripe pattern, unlike the color filter arrangement 500. In the color filter arrangement 510, R and B pixels are arranged on a diamond lattice (i.e., skew lattice) at a two-pixel period in the horizontal direction and at a one-pixel period in the vertical direction.
FIG. 18B shows spatial resolution characteristics of the respective G, R, and B pixels in the color filter arrangement 510. As shown in this figure, the resolution of the luminance signal is relatively high in the vertical and oblique directions; however, the resolution of the luminance signal is not sufficient in the horizontal direction.
The two-dimensional solid-state imaging apparatuses using the above-mentioned color filter arrangements 500 and 510 are of a progressive scan reading type or an equivalent type thereof, and the pixels are arranged in the horizontal and vertical lattice. Therefore, there is a limit to spatial resolution characteristics in any color filter arrangement.
In the case of using an X-Y scan reading type apparatus as a two-dimensional solid-state imaging apparatus in place of a CCD, the degree of freedom of the pixel arrangement becomes larger. For example, FIG. 19A shows a color filter arrangement 520 of an amplifier-type two-dimensional solid-state imaging apparatus of a progressive scan reading type using an X-Y scan reading method. The color filter arrangement 520 as shown in this figure is described, for example, in xe2x80x9cBCMDxe2x80x94An Improved Photosite Structure for High-Density Image Sensorsxe2x80x9d by J. Hynecek, IEEE Trans. on Electron Devices, Vol. 38, No. 5, May, 1991.
As shown in FIG. 19A, assuming that an arrangement in a horizontal line represents a xe2x80x9crowxe2x80x9d, the odd-number row (as counted from the topmost row) and the even-number row (as counted from the topmost row) in the vertical direction are shifted from each other by a 1/2 pixel pitch in the horizontal direction in the color filter arrangement 520. The respective G, R, and B pixels are arranged in each row in the order of R-G-B at a three-pixel period. Furthermore, the respective G, R, and B pixels are arranged in such a manner that identical color pixels are shifted by a 3/2 pixel pitch in the odd-number row and the even-number row. Thus, as shown in FIG. 19B, the spatial resolution characteristics of each color pixel match with each other. Relatively balanced resolution is obtained in the G, R, and B pixels. However, the horizontal resolution is not sufficient.
In the case where a color image obtained in a two-dimensional solid-state imaging apparatus is taken in a personal computer, luminance signal pixels or G pixels are desirably placed in a square lattice (i.e., an orthogonal lattice in which a horizontal pitch is equal to a vertical pitch). However, the color filter arrangements 510 and 520 shown in FIGS. 18A and 19A cannot satisfy this requirement. If a horizontal pixel pitch L is prescribed to be xc2xd of a vertical pixel pitch M (i.e., L=M/2) in the color filter arrangement 510 shown in FIG. 18A, the above-mentioned requirement can be satisfied. However, when the horizontal pixel pitch L is substantially decreased, the performance of the two-dimensional solid-state imaging apparatus becomes likely to degrade. For example, in the case of a CCD type two-dimensional solid-state imaging apparatus, the amount of transferable signal charge is decreased, making it difficult to maintain a dynamic range.
In the case of an X-Y scan reading type solid-state imaging apparatus, the performance is more easily maintained as the pixel configuration becomes closer to a square or a circle as in the color filter arrangement 520 shown in FIG. 19A.
The color solid-state imaging apparatus of this invention includes: a plurality of pixels conducting photoelectric conversion arranged in a matrix and color filters disposed so as to correspond to the plurality of pixels, wherein the color filters include first filters of a first kind, second filters of a second kind, and third filters of a third kind, each kind of filter having spectral characteristics different from the others, the plurality of pixels are arranged at a pitch L in a first direction to form rows, and each of the rows is arranged at a pitch M/2 in a second direction orthogonal to the first direction, the pixels disposed in even-number rows are shifted in the first direction by L/2 from the corresponding pixels disposed in odd-number rows, the first filters are disposed so as to correspond to all the pixels arranged in the odd-number rows, the second filters are disposed so as to correspond to a half of the pixels arranged in the even-number rows at a predetermined period, and the third filters are disposed so as to correspond to the remaining pixels in the even-number rows.
In one embodiment of the invention, L=M.
In another embodiment of the invention, the second filters are disposed so as to correspond to every other pixel in each of the even-number rows.
In another embodiment of the invention, the second filters are disposed at every other pixel in each of the even-number rows, and in an even-number row next to one even-number row with one odd-number row interposed therebetween, the second filters are disposed with respect to the remaining pixels not corresponding to the pixels at which the second filters are disposed in the one even-number row.
In still another embodiment of the invention, the second filters are disposed at every other pixel in each of the even-number rows, and in an even-number row next to one even-number row with one odd-number row interposed therebetween, the second filters are disposed with respect to the remaining pixels corresponding to the pixels at which the second filters are disposed in the one even-number row.
In still another embodiment of the invention, the second filters and the third filters are alternately disposed on a row basis in every other even-number row.
In still another embodiment of the invention, the first filters are green filters, the second filters are red filters, and the third filters are blue filters.
In still another embodiment of the invention, the plurality of pixels disposed in a matrix are scanned in the first and second directions, whereby video signals are read from the plurality of pixels.
In still another embodiment of the invention, the apparatus comprises: a first scanning circuit for scanning the plurality of pixels in the first direction and a second scanning circuit for scanning the plurality of pixels in the second direction.
In still another embodiment of the invention, the first and second scanning circuits sequentially scan all the plurality of pixels disposed in a matrix in the first and second directions.
In still another embodiment of the invention, the apparatus comprises: a plurality of vertical signal lines for transmitting a video signal read from each of the pixels by scanning of the second scanning circuit and a plurality of memory devices provided with respect to each of the vertical signal lines, for holding the video signals on the vertical signal lines, wherein the first scanning circuit scans the plurality of memory devices to read an identical video signal of one pixel held by the memory device at least twice, thereby substantially increasing resolution in the second direction.
In still another embodiment of the invention, the plurality of memory devices include a first memory device group provided with respect to the pixels in the odd-number rows and a second memory device group provided with respect to the pixels in the even-number rows, a plurality of horizontal signal lines for transmitting video signals read from the first and second memory device groups are provided, the first scanning circuit reads an identical video signal of one pixel held by each of the memory devices of the first and second memory device groups at least twice at a predetermined period, and a timing at which a video signal output from one of the plurality of horizontal signal lines changes from a video signal in one horizontal row to a video signal in a subsequent horizontal row is different from a timing at which a video signal output from another horizontal signal line different from the one of the plurality of horizontal signal lines changes from a video signal in one horizontal row to a video signal in a subsequent horizontal row.
Hereinafter, the function of the present invention will be described.
In the above-mentioned color filter arrangement, the G pixels (first color filters) which largely occupy a luminance signal are placed in a lattice with a predetermined interval in the first and second directions. Assuming that the first direction is a horizontal direction and the second direction is a vertical direction, high resolution can be obtained in the horizontal, vertical, and oblique directions. Furthermore, the R and B pixels (second and third color filters) can respectively provide spacial resolution which is xc2xd of that of the G pixels. Therefore, well-balanced color resolution can be obtained. Furthermore, in the case of L=M, the G pixels are placed in a square lattice and luminance signals in a square pixel arrangement can be obtained, so that an arrangement suitable for taking in a color image into a personal computer can be obtained.
Thus, the invention described herein makes possible the advantage of providing a novel color solid-state imaging apparatus of a progressive scan reading type which is capable of obtaining high color reproducibility and high spatial resolution by using a single plate coloring method.